A Virtual Router Redundancy Protocol (VRRP) network element (e.g., a VRRP router), is a collection of physical network devices that support the VRRP protocol. A VRRP virtual instance includes one physical network device operating as the master network device of the VRRP virtual network element and one or more other physical network devices operating as backup network devices of the VRRP virtual network element. In a VRRP group (i.e., VRRP network element), only the master device is enabled to accept subscriber traffic and forward it to an external network such as the Internet. Subscriber traffic directed at any of the backup devices is discarded.
A master network device is selected among the physical network devices in the VRRP instance based on priorities assigned to the physical devices. When a physical network device switches state from being a backup network device to a master network device, the master network device is required to send gratuitous Address Resolution Protocol (ARP) messages to notify the subscriber circuits of its virtual Media Access Control (MAC) address and virtual Internet Protocol (IP) address of the VRRP virtual device. The gratuitous ARP messages cause the subscriber circuits to update their bridging tables. The updated bridging tables cause subscriber traffic to be properly routed to the master network device instead of a backup router. In addition, a master network device periodically sends VRRP Advertisement (Ad) messages to all backup network devices of the VRRP virtual group notifying the backup network devices of the master device running status.
When the master device or any one of its links fail, the master network device (router) switches to being a backup network device. A new master network device is then selected based on priorities as discussed above. The new master network device sends gratuitous ARP messages to the subscriber circuits, causing traffic to be directed to the new master device, instead of the “original” master device.